In the past, readouts of instantaneous speed and elapsed mileage for bicycles have been possible with mechanically driven speedometers using a gear-driven worm on one of the wheels. Drag, noise, wear and limited readout information have been cause for complaints.
More recently, electronic cycle computers have replaced these old mechanically driven speedometers. They have a central computer, a clock, a liquid crystal display, and can gather and display a wide variety of information through a frictionless non-mechanical interface between the bicycle or rider and the computer itself. Typically, there are one or more magnets on one of the wheels and possibly on the crank arm, and a sensor coil or reed switch attached to the frame.
These new electronic cycle computers have basic speedometer capabilities including current speed and resettable trip and total distance displays. Generally, they have a built-in stop watch enabling a rider to calculate average speed at the end of a ride, although some have an average speed function which does this automatically. Others display additional information such as maximum speed, pedaling cadence, and even heart beat rate which is increasingly recognized as an important parameter for training racers and for those who ride for health and fitness.
At least four user categories are developing for these cycle computers: the serious, competitive, professional or non-competitive racing cyclist; the tourer, who may ride 100 miles or more a day; the casual cyclist; and children.
These are, of course, used while riding a bicycle. Use, setting and resetting must not require the rider to remove his or her hand from the handlebar or divert attention from the road or from traffic especially at those times when visibility is impaired by riding directly into the rising or setting sun; or by smoke, fog, haze or darkness. Conventional cycle computers require the rider to divert attention from the road and other traffic to the computer face, to remove one hand from the handlebar and use the index finger to activate the mode selection and control buttons. With only one hand on the handlebar, steering control can be dangerously reduced. To visually find the computer and locate the appropriate mode and control buttons, attention can be dangerously diverted from the road and traffic.